One of the most fundamental processes necessary for normal host defence is the regulated trafficking of leukocytes out of the vasculature. This system is designed to allow normal recirculation of leukocytes, yet because it enables the rapid extravasation of leukocytes at sites of injury it is one of the central pathogenic mechanisms of inflammatory, respiratory and autoimmune diseases in mammals. Cell adhesion is a key factor in this process, and it is particularly relevant to the present invention regarding the cell/cell and cell/matrix binding of hematopoietic cells containing VLA-4.
VLA-4 is a member of a superfamily of cell surface macromolecular receptors called integrins, which are non-covalent heterodimeric complexes consisting of an .alpha. subunit and a .beta. subunit (Hemler, Ann. Rev. Immunol., 8, p.365, 1990). Eighteen different a subunits have been identified and labeled .alpha..sub.1 -.alpha..sub.10, .alpha..sub.L, .alpha..sub.M, .alpha..sub.X, .alpha..sub.D, .alpha..sub.LRI, .alpha..sub.IIB, .alpha..sub.V and .alpha..sub.E ; while nine different .beta. subunits have been identified and labeled .beta..sub.1 -.beta..sub.9. Each integrin molecule can be categorized into a subfamily based on the type of its .alpha. and .beta. subunits.
The .alpha..sub.4.beta..sub.1 integrin, VLA-4, is an integrin constitutively expressed by all leukocytes (e.g., monocytes, lymphocytes, basophils, eosinophils, mast cells and macrophages) except polymorphonuclear leukocytes. The binding of this integrin to one of its ligands has a number of known cell adhesion and activation functions (Hemler, Ann. Rev. Immunol., 8, p.365, 1990; Walsh et al., Clin. and Exp. Allergy, 25, p. 1128, 1995; Huhtala et al., J. Cell Biol., 129, p. 867, 1995). In particular, it is a receptor for the cytokine-inducible endothelial cell surface protein known as vascular cell adhesion molecule-1 (VCAM-1), and for the alternatively spliced forms of the extracellular matrix protein fibronectin (FN) containing the CS-1 domain (Ruegg et al., J. Cell Biol., 177, p. 179, 1991; Wayner et al., J. Cell Biol., 105, p. 1873, 1987; Kramer et al., J. Biol. Chem., 264, p.4684, 1989; Gehlsen et al., Science, 24, p. 1228, 1988). The importance of VLA-4 cell adhesion interactions has been established by the use of specific monoclonal antibody (mAb) antagonists of the a subunit of VLA-4, which have demonstrated that inhibitors of VLA-4 dependent cell adhesion prevent or inhibit numerous inflammatory, respiratory and autoimmune pathological conditions (Chisholm et al., Eur. J. Immunol., 23, p. 682, 1993; Lobb et al., J. Clin. Invest, 94, p. 1722, 1994; Richards et al., Am. J. Respir. Cell Mol. Biol., 15, p.172, 1996; Soiluhanninen et al., J. Neuroimmunol., 72, p. 95, 1997; Sagara et al., Int. Arch. Allergy Immunol., 112, p.287, 1997; Fryer et al., J. Clin. Invest., 99, p. 2036, 1997). In addition, confirmation that this pathological processes can be inhibited with agents other than antibodies has been observed in animal models following treatment with a synthetic CS-1 peptide or a small molecule peptide inhibitor of VLA-4 (Ferguson et al., Proc. Natl. Acad. Sci., 88, p.8072, 1991; Wahl et al., J. Clin. Invest., 94, p.655, 1994; Molossi et al., J. Clin. Invest., 95, p.2601, 1995; Abraham et al., Am. J. Respir. Crit. Care Med., 156, p. 696, 1997; Jackson et al., J. Med. Chem., 40, p. 3359, 1997).